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PDS_VERSION_ID = PDS3
RECORD_TYPE = FIXED_LENGTH
RECORD_BYTES = 80
OBJECT = INSTRUMENT
INSTRUMENT_HOST_ID = "MGN"
INSTRUMENT_ID = "RDRS"
OBJECT = INSTRUMENT_INFORMATION
INSTRUMENT_NAME = "RADAR SYSTEM"
INSTRUMENT_TYPE = "RADAR"
INSTRUMENT_DESC = "
Instrument Specifications
=========================
The radar was manufactured by Hughes Aircraft Company and the
'build date' is taken to be 1989-01-01. The radar dimensions
were 0.304 by 1.35 by 0.902 (height by length by width in
meters) and the mass was 126.1 kg.
Instrument Id : RDRS
Instrument Host Id : MGN
Pi Pds User Id : GPETTENGILL
Instrument Name : RADAR SYSTEM
Instrument Type : RADAR
Build Date : 1989-01-01
Instrument Mass : 126.100000
Instrument Length : 1.350000
Instrument Width : 0.902000
Instrument Height : 0.304000
Instrument Manufacturer Name : HUGHES AIRCRAFT
For more information on the radar system see the papers by
[JOHNSON1990] and [SAUNDERSETAL1990].
Instrument Overview
===================
The Magellan radar system included a 3.7 m diameter high gain
antenna (HGA) for SAR and radiometry and a smaller fan-beam
antenna (ALTA) for altimetry. The system operated at 12.6 cm
wavelength. Common electronics were used in SAR, altimetry, and
radiometry modes. The SAR operated in a burst mode; altimetry
and radiometry observations were interleaved with the SAR
bursts.
Between SAR bursts (typically several times a second) groups of
altimeter pulses were transmitted from a dedicated fan-beam
altimeter antenna directed toward the spacecraft's nadir. The
altimeter pulses were identical in waveform and bandwidth to the
SAR pulses, resulting in a range accuracy of better than 15 m.
The pulse-repetition rate and burst duration differed between
the two modes.
Radiometry data were obtained by spending a portion of the time
between SAR bursts and after altimeter operation in a passive
(receive-only) mode, with the HGA antenna capturing the
microwave thermal emission from the planet. Noise power within
the 10-MHz receiver bandwidth was detected and accumulated for
50 ms. To reduce the sensitivity to receiver gain changes in
this mode, the receiver was connected on alternate bursts first
to a comparison dummy load at a known physical temperature and
then to the HGA. The short-term temperature resolution was
about 2 K; the long-term absolute accuracy after calibration was
about 20 K.
Science Objectives
==================
See MISSION_OBJECTIVES_SUMMARY under MISSION.
Operational Considerations
==========================
The Magellan radar system was used to acquire radar back-scatter
(SAR) images, altimetry, and radiometry when the spacecraft was
close to the planet. Nominal operation extended from about 20
minutes before periapsis until about 20 minutes after periapsis.
In the SAR mode output from the radar receiver was sampled,
blocks of samples were quantized using an adaptive procedure,
and the results were stored on tape. In the altimetry mode
samples were recorded directly, without quantization.
Radiometry measurements were stored in the radar header records.
During most of the remainder of each orbit, the HGA was pointed
toward Earth and the contents of the tape recorder were
transmitted to a station of the DSN at approximately 270
kilobits/second. SAR, altimetry, and radiometry data were then
processed using ground software into images, altimetry profiles,
estimates of backscatter coefficient, emissivity, and other
quantities.
Calibration Description
=======================
The radar was calibrated before flight using an active
electronic target simulator [CUEVAS1989].
Platform Mounting Descriptions
==============================
The spacecraft +Z axis vector was in the nominal direction of
the HGA boresight. The +X axis vector was parallel to the
nominal rotation axis of the solar panels. The +Y axis vector
formed a right-handed coordinate system and was in the nominal
direction of the star scanner boresight. The spacecraft
velocity vector was in approximately the -Y direction when the
spacecraft was oriented for left-looking SAR operation. The
nominal HGA polarization was linear in the y-direction.
Cone Offset Angle : 0.00
Cross Cone Offset Angle : 0.00
Twist Offset Angle : 0.00
The altimetry antenna boresight was in the x-z plane 25 degrees
from the +Z direction and 65 degrees from the +X direction. The
altimetry antenna was aimed approximately toward nadir during
nominal radar operation. The altimetry antenna polarization was
linear in the y-direction.
The medium gain antenna boresight was 70 degrees from the +Z
direction and 20 degrees from the -Y direction. The low gain
antenna was mounted on the back of the HGA feed; it's boresight
was in the +Z direction and it had a hemispherical radiation
pattern.
Principal Investigator
======================
The Principal Investigator for the radar instrument was Gordon
H. Pettengill.
Instrument Section / Operating Mode Descriptions
================================================
The Magellan radar system consisted of the following sections,
each of which operated in the following modes:
Section Mode
-------------------------------------------
SAR Synthetic Aperture Radar (SAR)
ALT Altimetry
RAD Radiometry
(1) SAR Characteristics
-----------------------
In the Synthetic Aperture Radar mode, the radar transmitted
bursts of phase-modulated pulses through its high gain
antenna. Echo signals were captured by the antenna, sampled
at the receiver output, and stored on tape after being
quantized to reduce data volume. Pulse repetition rate and
incidence angle were chosen to meet a minimum signal-to-noise
ratio requirement (8 dB) for image pixels after ground
processing. Multiple looks were used in processing to reduce
speckle noise. Incidence angles varied from about 13 degrees
at the pole to about 44 degrees at periapsis during normal
mapping operations (e.g., Cycle 1); but other 'look angle
profiles' were used during the mission.
Peak transmit power : 350 watts
Transmitted pulse length : 26.5 microsecs
Pulse repetition frequency : 4400-5800 per sec
Time bandwidth product : 60
Inverse baud width : 2.26 MHz
Data quantization (I and Q) : 2 bits each
Recorded data rate : 750 kilobits/sec
Polarization (nominal) : linear horizontal
HGA half-power full beam width : 2.2 deg (azimuth)
: 2.5 deg (elev)
one-way gain (from SAR RF port) : 35.7 dBi
System temperature (viewing Venus) : 1250 K
Surface resolution (range) : 120-360 m
(along track) : 120-150 m
Number of looks : 4 or more
Swath width : 25 km (approx)
Antenna look angle : 13-47 deg
Incidence angle on surface : 18-50 deg
Data Path Type : RECORDED DATA
PLAYBACK
Instrument Power Consumption : UNK
(2) ALT Characteristics
-----------------------
After SAR bursts (typically several times a second) groups of
altimeter pulses were transmitted from a dedicated fan beam
altimeter antenna (ALTA) directed toward the spacecraft's
nadir. Output from the radar receiver was sampled, and the
samples were stored on tape for transmission to Earth. During
nominal left-looking SAR operation the ALTA pointed
approximately 20 deg to the left of the spacecraft ground
track at periapsis and about 10 deg to the right of the ground
track near the north and south pole.
Data quantization (I and Q) : 4 bits each
Recorded data rate : 35 kbs
Polarization : linear
ALTA half-power full beamwidth
(along track): 11 deg
(cross track): 31 deg
one-way gain referenced to
ALT RF port : 18.9 dBi
ALTA offset from HGA : 25 deg
Burst interval : 0.5-1.0 sec
duration : 1.0 millisec
Dynamic range : 30 dB (or more)
Data Path Type : RECORDED DATA
PLAYBACK
Instrument Power Consumption : UNK
(3) RAD Characteristics
-----------------------
Radiometry measurements were made by the radar receiver and
HGA in a receive-only mode that was activated after the
altimetry mode to record the level of microwave radiothermal
emission from the planet. Noise power within the 10-MHz
receiver bandwidth was detected and accumulated for 50 ms. To
reduce the sensitivity to receiver gain changes in this mode,
the receiver was connected on alternate bursts first to a
comparison dummy load at a known physical temperature and then
to the HGA. The short-term temperature resolution was about 2
K; the long-term absolute accuracy after calibration was about
20 K. At several times during the mission, radiometry
measurements were carried out using known cosmic radio
sources.
Receiver Bandwidth : 10 MHz
Integration Time : 50 millisecs
Polarization (nominal) : linear horizontal
Data Quantization : 12 bits
Data Rate : 10-48 bits/sec
HGA half-power full beam width : 2.2 deg
System temperature (viewing Venus) : 1250 K
Antenna look angle : 13-47 deg
Incidence angle on surface : 18-50 deg
Surface resolution (along track) : 15-120 km
(cross track) : 20-125 km
Data Path Type : RECORDED DATA PLAYBACK
Instrument Power Consumption : UNK "
END_OBJECT = INSTRUMENT_INFORMATION
OBJECT = INSTRUMENT_REFERENCE_INFO
REFERENCE_KEY_ID = "CUEVAS1989"
END_OBJECT = INSTRUMENT_REFERENCE_INFO
OBJECT = INSTRUMENT_REFERENCE_INFO
REFERENCE_KEY_ID = "JOHNSON1990"
END_OBJECT = INSTRUMENT_REFERENCE_INFO
OBJECT = INSTRUMENT_REFERENCE_INFO
REFERENCE_KEY_ID = "SAUNDERSETAL1990"
END_OBJECT = INSTRUMENT_REFERENCE_INFO
END_OBJECT = INSTRUMENT
END